The availability of high-precision measurements of gene expression are
critical for obtaining an understanding of the functioning of
bacterial regulatory networks. In recent years, fluorescent and
luminescent reporter genes have become popular tools for measuring
gene expression, as they make it possible to monitor in vivo and in
real time the adaptive response of the bacteria on the molecular
level. While reporter gene systems allow the dynamics of gene
expression to be measured with high precision and temporal resolution,
they do not provide information on all variables of interest
though. Additional technologies may complement those that we have
developed in our laboratory, such as mass-spectrometry tools in
proteomics and metabolomics that are able to quantify the amounts of
proteins and metabolites, respectively, in a cell at a given
time-point. The data sources thus obtained are important for both the identification of models of bacterial regulatory networks as well as the validation of model predictions.

Glucose concentration controls a bacterial billboard.A microplate containing a minimal medium (with glucose and acetate) is filmed during 36 hours. Wells contain E. coli bacteria which are transformed with a reporter plasmid containing the luciferase operon (luxCDABE) under control of the acs promoter . This promoter is positively regulated by the CRP-cAMP complex. When bacteria have metabolized all the glucose, the cAMP concentration increases quickly and activates the global regulator CRP which turns on the transcription of the luciferase operon producing the light. The glucose concentration increases from left to right on the microplate, so its consumption takes more time when going up the gradient and the letters appears one after the other . The luciferase protein needs reductive power (FMNH2) to produce light. At the end, when acetate has been depleted, there is no more carbon source in the wells. As a consequence, the reductive power falls and the "bacterial billboard" switches off.